Parkinson's disease is a common degenerative disease of the nervous system for the middle-aged and elderly. Dopamine receptor agonist is an important class of drugs used in treating Parkinson's disease. Currently, the dopamine receptor agonist in clinical use comprises dopamine agonist drugs such as rotigotine, pramipexole, ropinirole, pergolide, and cabergoline, etc.
Rotigotine, (S)-5,6,7,8-tetrahydro-6-[propyl[2-(2-thienyl)ethyl]amino]-1-naphthol, is represented by a molecular formula of C19H25NOS and has the following structure. In May 2007, the U.S. FDA approved its listing under the trade name NeuPro for the adjuvant treatment of early secondary Parkinson's disease and advanced Parkinson's disease.

An impurity of a drug refers to a substance in the drug, which has no therapeutic effect but may influences the stability or efficacy of the drug, even may be harmful to human health. The source of the impurities mainly comprises the followings: firstly, the impurities that might have been introduced during the production process, including unreacted starting materials, chemical derivatives of impurities contained in the starting materials, synthesis by-products and degradation products; and secondly, the impurities that might have been produced during storage when the drug physicochemical properties changed due to the external conditions. Adverse reactions produced in clinical use, in addition to being attributable to the pharmacological activity of the drug itself, sometimes may also be related to impurities present in the drug. Therefore, normative research on the impurity is directly related to the quality and safety of marketed drugs.
By understanding the chemical structure and synthetic pathway of the impurities and by identifying the parameters which affect the content of impurities in the end product, management of impurities in medicinal active substance may be greatly enhanced. To monitor the impurities in the medicinal active substance, it is required to establish a quality standard to determine suitable separation and detection conditions, so as to control the impurities well. In the quality standard, the currently widely used impurity detection methods mainly comprise high performance liquid chromatography (HPLC) and like.